Method for continuously producing tertiary butyl ethers of glycerol

ABSTRACT

The invention relates to a method for producing a mixture of substances comprising a higher tertiary butyl ether of glycerol, comprising the steps: acid-catalyzed reaction of isobutene with glycerol to form a reaction mixture, and extraction of at least part of the reaction mixture from step a by means of at least one solvent, wherein the solvent or the mixture of solvents comprises an ET(30) value of=35.0.

FIELD OF TECHNOLOGY

The present invention relates to a method for producing a mixture ofsubstances comprising higher tertiary butyl ethers of glycerol.Moreover, the invention relates to a fuel which is obtainable by thismethod.

BACKGROUND

Glycerol is a very versatile educt which is prevalently produced fromregrowing raw materials. Glycerol is formed in the production ofbiodiesel as a co-product of its transesterification. Should the demandfor biodiesel be growing within the next years then glycerol wereavailable at too low prices in amounts that would argue for employing itin industrial-scale products.

Thus, distillatively separating a product mixture of glycerol and of amixture of high-boiling substances does not make sense for both, energyand technology reasons. The spectrum of GTBE (tertiary butyl ethers ofglycerol) comprises three different etherification steps of which onlythe higher ethers (di- and triethers), also referred to as h-GTBE, canbe employed as an octane enhancer in fuel. The mono-ether has lessfavorable combustion properties and also tends to sediment in fuel.

U.S. Pat. No. 5,731,476 describes a sulfonic acid-catalyzed homogenousetherification. At this, reaction is carried on only to a low conversionrate at which the reaction mixture still is in bi-phase form. Unreactedglycerol, the catalyst and parts of the resulting mono-ethers areseparated in a decanter and are cycled back. Isobutene is stripped outof the organic phase and the liquid phase is extracted with water. Then,the extract is discarded and the raffinate of higher ethers is recoveredat the head of the extraction unit.

The method shows disadvantages in that the reaction is carried out atlow conversion rates to ensure a two-phase stream at the exit of thereactor. Furthermore, the stream entering the extraction phase consistsof less than 50% of mono-ethers; thus, almost half of the separatedreaction products gets discarded.

Thus, one object is to provide an improved method for producing and/orpurifying tertiary butyl ethers of glycerol which overcomes the existingdisadvantages at least partially and is in particular able to provide ahigher yield in many applications.

SUMMARY

According to the invention, a method for producing a mixture ofsubstances comprising higher tertiary butyl ethers of glycerol isproposed, comprising the steps:

-   -   a) Acid-catalyzed reaction of isobutene with glycerol to form a        reaction mixture;    -   b) extraction of at least part of the reaction mixture from        step a) by means of at least one solvent, wherein the solvent or        the mixture of solvents comprises an E_(T)(30) value of ≦35.0.

In applying the method according to the invention at least one of thefollowing advantages can be achieved for a multitude of applications:

The glycerol ether resulting from the method may be extracted with afuel and may be used as a mixture for combustion engines,

the glycerol ether may be obtained directly if a further purificationstep is added,

the formation of by-products such as mono-tertiary butyl ethers(ultimately to be discarded) may be reduced significantly (if necessaryby appropriate additional measures),

an inconvenient thermal separation of water and glycerol is avoided,

an inconvenient separation of the mono-ethers from the h-GTBE isavoided.

As defined by the present invention, higher tertiary butyl ethers ofglycerol are those ethers which may result from the reaction ofisobutene with glycerol. In particular, isobutene and glycerol may beused in the form of pure substances. In this process, a catalyst may beused to accelerate the reaction. Tertiary butyl ethers of glycerolinclude in particular those ethers, selected from the group consistingof 3-tert-butoxy-propane-1,2-diol, 2-tert-butoxy-propane-1,3-diol,1,3-di-tert-butoxy-propane-2-ol, 2,3-di-tert-butoxy-propane-1-ol,1,2,3-tri-tert-butoxy-propane. Among the range of these ethers,di-ethers and tri-ethers are referred to as so-called higher ethers.

In the present invention, the mixture of substances may consist of atleast one component of the tertiary butyl ethers of glycerol, a solventand/or a further compound. The mixture of substances may be in ahomogenous or a heterogenous state. Preferably, the mixture ofsubstances is used in the form of a solution.

The first step of the method according to the invention comprises anacid-catalyzed reaction of isobutene with glycerol to yield a reactionmixture. As defined by the present invention, an acid-catalyzed reactionmeans in particular the sub-stoichiometrical use of a proton donortogether with the respective educts isobutene and glycerol. At this, thecatalyst may be present in a molar concentration, based on the initialconcentration of glycerol, in the range of ≧0.5 mol % to ≦10 mol %,preferably in a range of ≧2 mol % to ≦8 mol %, and particularlypreferred in a range of ≧3 mol % to ≦6 mol %. The catalyst may be in ahomogenous or a heterogenous state. Preferably, the fraction of glyceroland mono-ether in the mixture of substances is within a range of ≧0 wt %to ≦5 wt %, preferably within a range of ≧0.1 wt % to ≦3 wt %, andparticularly preferred within a range of ≧0.5 wt % to ≦2 wt %.

As defined by the present invention, the reaction mixture resulting fromthis means in particular the reaction mixture in the state from thebeginning of the reaction until the equilibrium state and/or thetermination of the reaction. The reaction mixture may be in a homogenousor a heterogenous state. As defined by the present invention, the eductsused in the method for producing tertiary butyl ethers of glycerol arein a liquid phase and are preferably selected from the group consistingof the raw materials of the educts, glycerol and an isobutene containingmaterial stream, raw glycerol and isobutene or raw glycerol and anisobutene containing material stream. Reacting pure glycerol with pureisobutene or isobutene containing streams may be particularly preferredin this process.

The reaction may be carried out in a reaction unit. In particular, thereaction unit is comprised of an stirred vessel, a cascade of stirredvessels, a tube reactor, a liquid jet mixer und/or a static mixer. Anindividual stirred vessel or a cascade of stirred vessels may beparticularly preferred in this process.

In a variant of the invention, the reaction mixture, after having beenreacted at least partially, is freed from unreacted isobutene bystripping and/or by flashing at leaving the reaction unit in the form ofa material stream. According to a preferred embodiment of the invention,the separated isobutene may be cycled back into the reaction at leastpartially. According to an alternative preferred embodiment of theinvention, the isobutene or isobutene containing gas stream may bedischarged off the reaction unit.

Step b) of the method according to the invention comprises an extractionof at least part of the reaction mixture from step a) by means of atleast one solvent, wherein the solvent or the mixture of solventscomprises an E_(T)(30) value of ≦35.0.

Herein, an extraction is in particular defined as the process ofselectively dissolving, washing or leaching out certain substances astransition components of solid or liquid mixtures of substances by meansof liquid solvents. As defined by the present invention, extraction mayin particular refer to a liquid-liquid-extraction.

It is important to point out that in case, a mixture of solvents is usedin step b), individual components of this mixture (depending on themethod's application) may have a higher E_(T)(30) value. These mixturesare explicitly included within the scope of the method of the inventionas long as the E_(T)(30) value of the mixture as a whole comprises avalue of ≦35.0.

As defined by the present invention, a solvent mixture is a mixture ofat least two partially miscible components. That means that onecomponent may dissolve into the other at a fraction of ≧90 vol %,preferably of ≧98 vol %, and particularly preferred of ≧99 vol %.Preferably, the obtained solvent mixture comprises an E_(T)(30) value of≦35.0.

Two liquid phases are participating in a liquid-liquid-extraction (LLE),in which the substance to be extracted, i.e. the valuable substance S,is dissolved out of the existent carrier liquid mixture by means of asolvent L. After a completed transfer of the valuable substance from thedonor phase to the receiving solvent, a mechanical phase separationyields the raffinate R, which is depleted of the valuable substance, andthe extract phase E, which is rich in valuable substance. In contrast toother separation processes, LLE does not result in an individuallyseparated mixture component but in a solvent-loaded mixture. In mostcases, this mixture may further be separated in subsequent processsteps.

“E_(T)(30) value” refers to the polarity of a solvent; within the scopeof this invention, however, reference is made to the values published byReichart; Dimroth, Fortschr. Chem. Forsch. 1969, 11, 1-73, ReichartAngew. Chem. 1979, 91, 119-131, and cited in: March, Advanced OrganicChemistry, 4th ed., J. Wiley & Sons, 1992, table 10.13, p. 361.

Preferably, the extraction is carried out with at least one solventwhich has an E_(T)(30) value of ≦33, and/or wherein the solventpreferably has a miscibility gap with water.

Preferably, the extraction is carried out with at least one solventwhich has an E_(T)(30) value of ≦32.0, even more preferably of ≦31.5.

Particularly preferred solvents are those, selected from the group ofalkanes, cycloalkanes, alkenes, cycloalkenes, alkines, cycloalkinesand/or the aromatic C6-C14 carbons.

As defined by the present invention, solvents are in particular selectedfrom the group, comprising 2-methylbutane, n-pentane, n-hexane,1-hexene, 1-hexine, n-heptane, n-octane, n-nonane, benzene,methylbenzene, toluene, (trifluoromethyl)benzene, 1,4-dimethylbenzene,p-xylene, 1,3,5 -trimethylbenzene, n-decane, n-dodecane, cyclohexane,cyclohexene, cis-decahydronaphthalene, 1,2,3,4-tetrahydronaphthalene,vinylbenzene, diethyl ether, bis(2-chloroethyl)ether, tetrahydrofurane,ethyl vinyl ether, di-n-propyl ether, diisopropyl ether, di-n-butylether, tert-butyl methyl ether, tert-amyl methyl ether,2-methoxy-2-methylbutane and/or carbon disulfide.

In a variant, the solvent may be selected from the group of diesel fuel,kerosine, petrol, light petrol, synthetic petrol, alkylate based petrol,biodiesel, ethanol-fuel, cellulose-ethanol, butanol, liquid gas,methanol, plant oil, heavy fuel oil, benzene, petrol and benzenemixtures, gasoil, motor petroleum.

In one embodiment of the method according to the present invention, thevolume ratio of solvent and reaction mixture of step a) is within arange of ≦0.8:1 and ≦1.5:1. In a liquid-liquid-extraction, themono-ether compounds may be more easily separated from the mixture bymeans of the glycerol phase such that the mono-ether may preferably stayin the polar phase.

In a further variant of the invention, the molar ratio (mol:mol) of theeducts isobutene and glycerol may be in a range of ≧1:0.5 and ≦1:5,preferably in a range of ≧1:1 and ≦4, and particularly preferred in arange of ≧1:1.5 and ≦1:3.5. Like this, the conversion of isobutene maybe increased. This proves to be particularly favorable with mixturessuch as raffinate I. As one advantage, the gas exhaust contains littleisobutene because, as in the production of ethyl tertiary butyl ether,for example, an isobutene conversion of 99% may be obtained only by avery laborious twofold reactive rectification.

As defined by the present invention, “raffinate I” is in particular amixture of isobutene plus at least one further substance, selected fromthe group of isobutane, n-butane, 2-butene (cis and/or trans), 1-buteneand butadiene.

In a further alternative embodiment of the method according to thepresent invention, the molar ratio (mol:mol) of isobutene and the highertertiary butyl ethers of glycerol from step a) is within a range of≧0.1:1 and ≦1:1. Like this, the conversion of isobutene may beincreased. This proves to be particularly advantageous with mixtureslike raffinate I, for example. As one advantage, the gas exhaustcontains little isobutene because, as in the production of ethyltertiary butyl ether, for example, an isobutene conversion of 99% may beobtained only by a very laborious twofold reactive rectification.

In a further embodiment of the method according to the presentinvention, the temperature of the reaction mixture of step a) is between≧60° C. and ≦130° C., preferably in a temperature range of between ≧70 Cand ≦120° C., and particularly preferred in a temperature range ofbetween ≧80° C. and ≦110° C. At this temperature, the reaction progresswith respect to the yield and reaction time is improved in manyapplications.

In a further embodiment of the method according to the presentinvention, the conversion is effected at a pressure of ≧10 bar to ≦20bar. Advantageously, the compounds, which are in the form of gases undernormal conditions, may be liquified and used as solvents in thispressure range. Another advantage in many applications of the inventionlies in the fact that this pressure range is favorable for economicallyoperating the reaction system because it corresponds to its internalpressure and, thus, does not have to be produced by compression or pumpperformance.

In a further embodiment of the method according to the presentinvention, the acid from step a) has a pKa value of ≦2. As defined bythe present invention, the term “acid” comprises substances which canact as a proton donor. It may also refer to a mixture of acids whichhave a pKa value of ≦2. In particular, the acid is one, comprisinghydrochlorid acid, sulfuric acid and/or sulfonic acid. Preferably,p-toluenesulfonic acid, methanesulfonic acid and/or benzenesulfonic acidmay be used.

In a further embodiment of the method according to the presentinvention, the higher ethers are extracted out of the liquid reactionproduct by means of a carbon containing stream which may be petrol, purehydrocarbon and/or a naphtha.

In one variant, the higher ethers may be extracted with petrol plus anaddition of a glycerol containing stream or with pure hydrocarbon plusan addition of a glycerol containing stream. The extraction unit may berealized by means of several mixer-settler-units, by extraction columnsor by interconnecting both of them. The stream conduction may be bycross flow, counter flow or by counter flow distribution.

In a further variant, the extract stream may be processed thermally, andthe extraction medium may be cycled back into the extraction process.Advantageously, this leads to savings in extraction medium and, thus, toa more cost-effective production of the substance mixture of theinvention.

In a further embodiment of the method according to the presentinvention, the acid-catalyzed reaction is a homogenous catalysis,wherein the catalyst and the educts may be in solution at least duringthe catalytical step of the reaction.

Further, an object of the invention is a fuel which can be obtained bythe method of the invention, comprising at least part of the reactionmixture from step a) and at least one solvent.

Another object of the invention relates to the use of the fuel incombustion engines, turbines or combustion plants.

The aforementioned and claimed method of the invention, as described inthe embodiment examples, is not subject to specific exclusion provisionswith respect to its size, system design, material selection andtechnical conception such that the selection criteria known to theapplication field may be applied unrestrictedly.

Further details, features and advantages of the object of the inventionmay be deduced from the subclaims and the following description of thedrawings relating thereto, in which several embodiments of the methodaccording to the present invention are depicted by way of example.

BRIEF DESCRIPTION

The present invention will be further explained by means of specificembodiments of the method with reference to the following drawings,without being restricted to this, wherein:

FIG. 1 shows a method for producing a fuel comprising higher ethers; and

FIG. 2 shows an alternative method for producing higher ethers.

DETAILED DESCRIPTION

FIG. 1 shows an assembly of the various process steps according to apreferred embodiment of the method. Following an optional precleansing,the educt isobutene is conducted to an appropriate reaction unit (A) viathe stream (1), together with recycled isobutene (4) and recycledglycerol, mono-ether and catalyst (14). In a downstream process step,the reaction product (3) is freed of unreacted isobutene in a strippingcolumn (B) (or alternatively a flash), which is then recycled to thereaction (4).

The liquid phase (5), which is led off the stripping column (B), isconducted further to a process step of liquid-liquid-extracting in acontinuous extraction unit (C). As an extraction medium, which issupplied via stream (7), the fuel to be upgraded qualitatively may beemployed directly.

To enhance the polar phase of the extraction, at least part of theglycerol to be supplied to the system is fed into the continuousextraction unit (C) via stream (6), if applicable, as this is notabsolutely necessary for the process and dependent on the application.From the extraction unit (C), mixture (8) is supplied to the settlingunit (C′). Depending on the design, this may occur via pumps from onecontainer to the next (mixer-settler) or simply via an overflow weir(decanter).

In this embodiment, the head stream (10) of the continuous extractionunit is supplied to the extraction column and is extracted with afurther stream of fresh glycerol (11). The head stream (13) of thesystem unit (D) may be used directly as a fuel or may be diluted to thecorresponding volume fraction of the higher ethers. The extracts rich inglycerol (9), (12) are cycled back into the reactor (14).

It should be noted that the head stream (10) may be made further use ofdirectly, without further extraction, which depends on the application.

FIG. 2 shows a variant of the process according to an alternativepreferred embodiment of the invention, in order to isolate the higherethers. Herein, the streams and system units of FIG. 2 correspond to theprocess of FIG. 1, if not indicated otherwise.

In the process of FIG. 2, the unpolar raffinate (13) is supplied to aretification unit (E), or optionally a flash, to thermally separate theextraction medium in order to recycle it. The separated, low-boilingextraction medium is recycled via stream (7) into the continuousextraction unit (C), and the higher ethers as high boiling componentsare recovered via stream (15).

The individual combinations of the components and the features of theaforementioned embodiments are exemplary only; the exchange and thesubstitution of these teachings with other teachings, which are includedin this disclosure, and with the cited disclosures are also explicitlycontemplated. It will be apparent to those skilled in the art thatvariations, modifications and other embodiments than those describedherein may be made thereto without departing from the spirit and scopeof the invention. Accordingly, the above description is by way ofexample and not to be construed as limiting. The word “comprising”, asused in the claims, does not preclude other constituents or steps. Theindefinite article “a/an” does not preclude the meaning of a plural. Themere fact that certain measures are cited in mutually different claimsdoes not illustrate that a combination of these measures may not beutilized in an advantageous manner. The scope of the invention isdefined by the following claims and the associated equivalents.Furthermore, the used reference signs are not limiting the claimed scopeof the invention.

1. A method for producing a mixture of substances comprising highertertiary butyl ethers of glycerol, comprising the steps: a) reacting anacid-catalyzed reaction of isobutene with glycerol to form a reactionmixture; and b) extracting at least part of the reaction mixture fromstep a) by means of at least one solvent, wherein the at least onesolvent or a mixture of solvents comprises an E_(T)(30) value of ≦35.0.2. A method according to claim 1, wherein a volume ratio of the at leastone solvent and the reaction mixture of step a) is within a range of≦0.8:1 and ≦1.5:1.
 3. A method according to claim 1, wherein a molarratio of the educts isobutene and glycerol is in a range of ≧1:0.5 and≦1:5.
 4. A method according to claim 1, wherein the a temperature of thereaction mixture of step a) is between ≧60° C. and ≦130° C.
 5. A methodaccording to claim 1, wherein a conversion is effected at a pressure of≧10 bar to ≦20 bar.
 6. A method according to claim 1, wherein the acidfrom step a) has a pKa value of ≦2.
 7. A method according to claim 1,wherein the higher tertiary butyl ethers of glycerol are extracted outof a liquid reaction product by means of a carbon containing stream. 8.A method according to claim 1, wherein the acid-catalyzed reaction fromstep a) is a homogenous catalysis.
 9. A fuel, obtainable by a methodaccording to claim 1, comprising at least part of the reaction mixturefrom step a) and at least one solvent.
 10. The fuel of claim 9, whereina use of the fuel includes combustion engines, turbines or combustionplants.